The number of standardized tests U.S. public school students take has exploded in the past decade, with most schools requiring too many tests of dubious value, according to the first comprehensive survey of the nation’s largest districts.

A typical student takes 112 mandated standardized tests between pre-kindergarten classes and 12th grade, a new Council of the Great City Schools study found. By contrast, most countries that outperform the United States on international exams test students three times during their school careers.

In a video posted to Facebook by the White House on Saturday, President Obama pledged to take steps to reduce testing overload.

In “moderation, smart, strategic tests can help us measure our kids’ progress in school, and it can help them learn,” Obama said. “But I also hear from parents who, rightly, worry about too much testing, and from teachers who feel so much pressure to teach to a test that it takes the joy out of teaching and learning, both for them and for the students. I want to fix that.”

The heaviest testing load falls on the nation’s eighth-graders, who spend an average of 25.3 hours during the school year taking standardized tests, uniform exams required of all students in a particular grade or course of study. Testing affects even the youngest students, with the average pre-K class giving 4.1 standardized tests, the report found.

The study analyzed tests given in 66 urban districts in the 2014-2015 school year. It did not count quizzes or tests created by classroom teachers, and it did not address the amount of time schools devote to test preparation.

It portrays a chock-a-block jumble, where tests have been layered upon tests under mandates from Congress, the U.S. Department of Education and state and local governments, many of which the study argues have questionable value to teachers and students. Testing companies that aggressively market new exams also share the blame, the study said.

“Everyone is culpable here,” said Michael Casserly, executive director of the Council of the Great City Schools. “You’ve got multiple actors requiring, urging and encouraging a variety of tests for very different reasons that don’t necessarily add up to a clear picture of how our kids are doing. The result is an assessment system that’s not very intelligent and not coherent.”

Ahead of the study’s release, the U.S. Department of Education offered a mea culpa of sorts, issuing a 10-page “action plan” to states and local districts that spells out ways to reduce redundant and low-quality testing. The department pledged to make money and staff available to help and promised to amend some of its policies.

“At the federal, state and local level, we have all supported policies that have contributed to the problem in implementation,” Education Secretary Arne Duncan said in a statement. “We can and will work with states, districts and educators to help solve it.”

The agency is recommending that states cap the amount of time devoted to test-taking to no more than 2 percent of class time. A similar proposal is part of the bill pending in the Senate to replace No Child Left Behind. Casserly cautioned against an arbitrary limit, saying he is concerned that states would indiscriminately lop off tests to meet a federal testing cap. A better approach, he said, would be a coordinated effort among all players — federal, state and local — to come up with a more thoughtful system.

The council’s report adds fuel to the national debate about testing that has spurred various “opt out” movements among parents and students and has put growing political pressure on Congress and state legislatures to cut back.

In one of the most notable attempts to reduce testing, Miami-Dade County Public Schools Superintendent Alberto Carvalho earlier this year cut the number of district-created end-of-course exams from 300 to 10 and eliminated them entirely for elementary schools.

“I believe in accountability,” said Carvalho, who runs the nation’s fourth-largest school district. “But fewer assessments of higher quality are better. . . . What we have now across the country is confusing, hard to navigate and, I believe, abusive of both teacher and student time.”

California eliminated its high school graduation test three weeks ago, joining Minnesota, Mississippi, Alaska, Rhode Island and South Carolina. Virginia has reduced its number of state-level tests, and Montgomery County, Md., last month put an end to its high school final exams.

Standardized testing has caused intense debate on Capitol Hill as lawmakers work to craft a replacement for No Child Left Behind. Testing critics tried unsuccessfully to erase the federal requirement that schools test in math and reading. Civil rights advocates pushed back, arguing that tests are an important safeguard for struggling students because publicly reported test scores illuminate the achievement gap between historically underserved students and their more affluent peers.

“For those of us who support annual assessments, it doesn’t mean we support this craziness,” said Kati Haycock, president of the Education Trust, an advocacy group focused on reducing the achievement gap. “There’s a clear problem here.”

Testing tends to be concentrated between February and May. The council’s study found numerous examples of redundancy, with students often taking an end-of-course test, an Advanced Placement test and a final exam for the same course.

In 40 percent of districts surveyed, test results aren’t available until the following school year, making them useless for teachers who want to use results to help guide their work in the classroom, Casserly said.

Jeffrey Cipriani teaches second grade at Orchard Gardens K-8 Pilot School in Boston. Even though his students are not in a grade that is required by federal law to be tested, the Boston Public Schools has him administer reading tests to his students three times a year. Because the tests are individual and can be as long as 90 minutes, it takes Cipriani about three weeks to test the whole class.

“It’s a colossal amount of time,” he said. “I probably spend about 60 hours not teaching reading but just sort of giving those assessments. They’re valuable but not that valuable.”

The study found no correlation between the amount of testing in a district and the way its students perform on the National Assessment of Educational Progress (NAEP), a federal test given every two years that is the only consistent measure of student achievement across state lines.

“We can’t assess our way to academic excellence,” Carvalho, of the Miami-Dade school system, said.

While public schools have been administering standardized tests for generations, the current buildup began after Congress passed No Child Left Behind in 2001 and required states to test all students in math and reading annually from third grade through eighth grade, and once in high school.

States that failed to make academic progress faced a series of consequences. States and districts responded by adding new tests during the school year to ensure students were on track.

“You prepare for the test to prepare for the test to prepare for the test,” said Robert Schaeffer of the National Center for Fair and Open Testing, a nonprofit organization critical of standardized testing.

To win a grant under the competitive Race to the Top program, or to receive a waiver from No Child Left Behind, states had to evaluate teachers based in part on student test scores. Since federal law required standardized tests only in math and reading in certain grades, states added tests in social studies, science, languages — even physical education — to have scores they could use to evaluate teachers.

“Many of the appalling things reported on here are the direct result of the way the federal government has approached this,” said Marc Tucker, president of the National Center on Education and the Economy. “The accountability system is what’s driving this and it’s fundamentally flawed.”

In its new guidance to states, the U.S. Department of Education tries to soften its emphasis on using test scores to evaluate teachers and urges states and local districts to cut down on redundant and low-quality tests.

The agency also pledged to work with states to amend waivers they have received under No Child Left Behind “to reduce testing in grades and subjects that are not subject to federal testing requirements and/or find alternative ways” to judge student achievement and use that to evaluate teachers.

“The time is now to take some new and meaningful steps to help schools deal with testing where it is unnecessary,” said John King, who is slated to succeed Duncan in January. “This is something the president and I have talked about, and it will be a key priority for me in our work with states and districts over the next 14 months.”